Methods for treating restless legs syndrome

ABSTRACT

The invention is directed to a method of treating restless legs syndrome in a subject, comprising administering a therapeutically effective amount of a carbamate compound, or pharmaceutically acceptable salt or amide thereof.

BACKGROUND OF THE INVENTION

The present invention relates a method of treating restless legs syndrome. More specifically, the present invention is directed to a method of using a carbamate compound alone or in combination with other medications, for the treatment of restless legs syndrome.

DESCRIPTION OF RELATED ART

Restless legs syndrome (RLS) is a chronic and progressive neurologic movement disorder characterized by the presence of 4 diagnostic criteria: 1) an urge to move the limbs with and without sensations; 2) worsening at rest; 3) improvement with activity; and 4) worsening in the evening or night (Bayard et al., 2008; Ondo, 2009). The sensations are always considered unpleasant but are not necessarily painful and tend to occur deep within the legs between the knee and ankle (Ondo, 2009). RLS has been reported to affect about 10% of adults with approximately one-third of those affected experiencing symptoms with moderate to severe intensity requiring treatment. There appears to be a genetic predisposition to RLS, especially in those with an early onset before 18 years of age (Bayard et al., 2008; Ondo, 2009).

One of the prevalent symptoms of RLS is the presence of periodic limb movements of sleep (PLMS). PLMS are defined as periodic instances of repetitive and stereotyped limb movements during sleep. About 80% of those with RLS show PLMS but PMLS is not exclusive to RLS (Bayard et al., 2008; Ondo, 2009). Many RLS treatments have been shown to reduce PLMS (Bayard et al., 2008). In addition, patients with RLS are more likely to be depressed (Hornyak, 2010) or anxious. Sleep patterns are also disturbed as individuals have trouble falling and maintaining sleep.

Current first line treatments of RLS include non-ergotamine dopamine agonists including pramipexole and ropinirole (Fulda & Wetter, 2005; Bayard et al., 2008). Side effects of these drugs include nausea, orthostasis, daytime somnolence and some augmentation. The Carbidopa/levodopa combination is also recommended due to the rapid onset of action but gastrointestinal issues, headache and augmentation are common side effects. Augmentation refers to the development of RLS symptoms of greater intensity occurring earlier in the day, in other parts of the body such as the arms or less relief with movement (Bayard et al., 2008; Ondo, 2009). Other treatments considered second line include gabapentin, opioids, benzodiazepine and ergotamine dopamine antagonists (cabergoline and pergolide). These may be treated in combination with non-ergotamine dopamine agonists. Gabapentin would be considered first line in patients with comorbid neuropathic pain and was also shown to improve sleep parameters including total sleep time, sleep efficiency, slow wave sleep and stage 1 sleep (Ondo, 2009). Opioids and benzodiazepines show high potential for abuse. In addition, daytime sleepiness is a common side effect of gabapentin and benzodiazepines. Treatment with ergotamine dopamine agonists increased the risk of cardiac valvulopathy, retroperitoneal, pericardial and pleuropulmonary fibrosis (Ferini-Strambi, 2009). Selective serotonin reuptake inhibitors are not recommended as these compounds tend to increase the symptoms of RLS including PLMS (Bayard et al., 2008; Hornyak, 2010). Bupropion, a dopamine and norepinephrine reuptake inhibitor, decreased the presence of PLMS and rapidly improved symptoms of RLS (Kim et al., 2005; Hornyak, 2010).

Consistent with the choice of dopamine agonists as first line treatment, patients with RLS have been shown to have some abnormalities in the dopaminergic system (Bayard et al., 2008; Ondo, 2009). Namely, there appears to be an enhanced circadian variation in dopamine activity in those with RLS compared to controls (Garcia-Borreguero et al., 2004; Bayard et al., 2008). Furthermore, iron content in both the substantia nigra and the putamen, was shown to be decreased in RLS patients compared to controls (Allen et al., 2001; Bayard et al., 2008). Iron is a cofactor with tyrosine hydroxylase, the enzyme that converts tyrosine to dopamine. Thus, RLS patients may show a dopaminergic activity imbalance.

Afferent systems have also been implicated in the pathophysiology of RLS. It has been reported that ratings of pin pricks of the lower limbs were significantly increased while pain thresholds were considered normal (Stiasny-Kolster et al., 2004). Thus, there appears to be a relation to the hyperalgesia subtype of neuropathic pain.

Accordingly, there is a need in the treatment of restless legs syndrome that would improve efficacy in the treatment of lower leg sensations, PLMS, sleep disturbances and other comorbidities including depression and neuropathic pain and reduce side effect profiles.

SUMMARY OF THE INVENTION

The present invention is directed to a method of treating restless legs syndrome comprising administering a therapeutically effective amount of a compound having Structural Formula (1) or a pharmaceutically acceptable salt thereof, to a mammal in need of treatment:

wherein,

R is selected from the group consisting of hydrogen, lower alkyl of 1 to 8 carbon atoms, halogen selected from F, Cl, Br and I, alkoxy of 1 to 3 carbon atoms, nitro group, hydroxy, trifluoromethyl, and thioalkoxy of 1 to 3 carbon atoms;

x represents the number of R, and is an integer of 1 to 3, with the proviso that R may be the same or different when x is 2 or 3;

R₁ and R₂ can be the same or different from each other and are independently selected from the group consisting of hydrogen, lower alkyl of 1 to 8 carbon atoms, aryl of 3 to 7 carbon atoms, arylalkyl of 3 to 7 carbon atoms, and cycloalkyl of 3 to 7 carbon atoms;

R₁ and R₂ can be joined to form a 5 to 7-membered heterocycle substituted with a member selected from the group consisting of hydrogen, alkyl of 1 to 8 carbon atoms, and aryl of 3 to 7 carbon atoms, wherein the heterocyclic compound comprises 1 to 2 nitrogen atoms and 0 to 1 oxygen atom, and the nitrogen atoms are not directly connected with each other or with the oxygen atom.

In another embodiment, the present invention provides a method of improving symptoms associated with restless legs syndrome in a subject, comprising the step of the administration, to a subject in need of such treatment, of a therapeutically effective amount a compound of the Formula (1) or a pharmaceutically acceptable salt thereof.

In further embodiment, the present invention provides a method of ameliorating or eliminating symptoms of restless legs syndrome in a subject, comprising the step of the administration, to a subject in need of such treatment, of a therapeutically effective amount a compound of the Formula (1) or a pharmaceutically acceptable salt thereof.

In additional embodiment, the present invention is directed to pharmaceutical composition for treating restless legs syndrome comprising a compound of the Formula (1) or a pharmaceutically acceptable salt thereof, as an active ingredient.

In another embodiment, the present invention provides a pharmaceutical composition for improving symptoms associated with restless legs syndrome in a subject, comprising a therapeutically effective amount a compound of the Formula (1) or a pharmaceutically acceptable salt thereof.

In further embodiment, the present invention provides a pharmaceutical composition for ameliorating or eliminating symptoms of restless legs syndrome in a subject, comprising a therapeutically effective amount a compound of the Formula (1) or a pharmaceutically acceptable salt thereof.

The compound having structural Formula (1) is an enantiomer substantially free of other enantiomers or an enantiomeric mixture wherein one enantiomer of the compound having structural Formula (1) predominates. One enantiomer predominates to the extent of about 90% or greater, and preferably about 98% or greater.

The enantiomer is (S) or (L) enantiomer as represented by Structural Formula (1a) or (R) or (D) enantiomer, as represented by Structural Formula (1b):

Preferably, R, R₁ and R₂ are all selected from hydrogen, which are shown in the following formula:

Embodiments of the invention include a method for using the enantiomer of Formula 1 substantially free of other enantiomers that is the enantiomer of Formula 1b or an enantiomeric mixture wherein the enantiomer of Formula 1b predominates. (Note: in the structural formula of Formula 1b below the amino group attached to the beta carbon projects into the plane of the paper. This is the dextrorotary (D) enantiomer that is of absolute configuration (R).)

DETAILED DESCRIPTION OF THE EMBODIMENT

These and other objects of the invention will be more fully understood from the following description of the invention and the claims appended hereto.

The present invention is directed to a method of treating restless legs syndrome comprising the administration of a therapeutically effective amount of a compound having structural Formula (1) or enantiomers, diastereomers, racemates or mixtures thereof, or hydrates, solvates and pharmaceutically acceptable salts and amides thereof, to a mammal in need of treatment:

wherein,

R is selected from the group consisting of hydrogen, lower alkyl of 1 to 8 carbon atoms, halogen selected from F, Cl, Br and I, alkoxy of 1 to 3 carbon atoms, nitro group, hydroxy, trifluoromethyl, and thioalkoxy of 1 to 3 carbon atoms;

x represents the number of R, and is an integer of 1 to 3, with the proviso that R may be the same or different when x is 2 or 3;

R₁ and R₂ can be the same or different from each other and are independently selected from the group consisting of hydrogen, lower alkyl of 1 to 8 carbon atoms, aryl of 3 to 7 carbon atoms, arylalkyl of 3 to 7 carbon atoms, and cycloalkyl of 3 to 7 carbon atoms;

R₁ and R₂ can be joined to form a 5 to 7-membered heterocycle substituted with a member selected from the group consisting of hydrogen, alkyl 1 to 8 carbon atoms, and aryl 3 to 7 carbon atoms, wherein the heterocyclic compound comprises 1 to 2 nitrogen atoms and 0 to 1 oxygen atom, and the nitrogen atoms are not directly connected with each other or with the oxygen atom.

The present method also includes the use of a compound selected from the group consisting Formula 1a or 1b, or enantiomers, diastereomers, racemates or mixtures thereof, or hydrates, solvates and pharmaceutically acceptable salts and amides thereof:

wherein Rx, R₁ and R₂ are the same as defined above.

The present method also preferably includes the use of the D (or dextrorotary) enantiomer (of absolute configuration R) selected from the group consisting of a compound of Formula 1 or an enantiomeric mixture thereof. In the structural formula of Formula 1b, the amino group attached to the beta carbon projects into the plane of the paper. This is the dextrorotary (D) enantiomer that is of absolute configuration (R).

Preferably, in the Structural Formula 1, R, R₁ and R₂ are hydrogen as represented by following Structural Formula:

O-carbamoyl-(D)-phenylalaninol is also named (R)-(beta-amino-benzenepropyl) carbamate monohydrochloric acid. For enantiomeric mixtures, wherein O-carbamoyl-(D)-phenylalaninol predominates, preferably, to the extent of about 90% or greater, and more preferably about 98% or greater.

The compounds of Formula 1 can be synthesized by methods known to a skilled person in the art. Some reaction schemes for synthesizing compounds of Formula (1) have been described in published; U.S. Pat. Nos. 5,705,640, 5,756,817, 5,955,499, and 6,140,532. Details of the above reactions schemes as well as representative examples on the preparation of specific compounds have been described in published; U.S. Pat. Nos. 5,705,640, 5,756,817, 5,955,499, 6,140,532, all incorporated herein by reference in their entirety.

The salts and amides of the compounds of Formula (1) can be produced by treating the compound with an acid (HX) in suitable solvent or by means well known to those of skill in the art.

From Structural Formula 1, it is evident that some of the compounds of the invention have at least one and possibly more asymmetric carbon atoms. It is intended that the present invention include within its scope the stereochemically pure isomeric forms of the compounds as well as their racemates. Stereochemically pure isomeric forms may be obtained by the application of art known principles. Diastereoisomers may be separated by physical separation methods such as fractional crystallization and chromatographic techniques, and enantiomers may be separated from each other by the selective crystallization of the diastereomeric salts with optically active acids or bases or by chiral chromatography. Pure stereoisomers may also be prepared synthetically from appropriate stereochemically pure starting materials, or by using stereoselective reactions.

During any of the processes for preparation of the compounds of the present invention, it may be necessary and/or desirable to protect sensitive or reactive groups on any of the molecules concerned. This may be achieved by means of conventional protecting groups, such as those described in Protective Groups in Organic Chemistry, ed. J. F. W. McOmie, Plenum Press, 1973; and T. W. Greene & P. G. M. Wuts, Protective Groups in Organic Synthesis, Third Edition, John Wiley & Sons, 1999. The protecting groups may be removed at a convenient subsequent stage using methods known from the art.

The present invention is based in part on the discovery that phenylalkylamino carbamates of Formula 1 discussed above have novel and unique pharmacological properties. These compounds have been shown in several animal models to have the ability to treat restless legs syndrome and improve, ameliorate or eliminate symptoms associated with restless legs syndrome.

Although the precise mechanism of action is not completely understood, it is known that these compounds do not work by the same mechanisms as most other known treatments for restless legs syndrome. For these reasons, the compounds of Formula 1 are especially suitable for use as sole or adjunctive treatment for restless legs syndrome and improvement, amelioration or elimination of symptoms associated with restless legs syndrome.

The symptoms associated with restless legs syndrome may include, but not be limited to lower leg sensations, periodic limb movements of sleep (PLMS), unpleasant leg sensation, urge to move, restlessness, sleep disturbances, excessive daytime sleepiness and the like.

Thus, these compounds can be safely used alone or in combination with other useful medications to provide enhanced efficacy and reduced side effects because smaller doses of each drug that could be used.

In one aspect, this invention relates to methods to treat restless legs syndrome; the method comprising administering to a subject suffering from restless legs syndrome a therapeutically effective amount of one or more of the carbamate compounds of the invention or a pharmaceutically acceptable salt or amides thereof, optionally with a pharmaceutically acceptable carrier, diluent, or excipient. The method may further comprise the step of identifying a subject suffering from restless legs syndrome before the administering step.

In another aspect, this invention also provides a method for diminishing, inhibiting or eliminating the symptoms of restless legs syndrome including lower leg sensations, periodic leg movements of sleep, unpleasant leg sensations, urge to move, restlessness, excessive daytime sleepiness, and sleep disturbances, in a subject suffering from restless legs syndrome which comprises administering to the subject an effective amount of carbamate compounds of the invention or a pharmaceutically acceptable salt or amides thereof to diminish, inhibit or eliminate said symptoms.

DEFINITIONS

For convenience, certain terms employed in the specification, examples, and appended claims are collected here.

It is to be understood that this invention is not limited to the particular methodology, protocols, animal species or genera, and reagents described, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention that will be limited only by the appended claims.

As used herein the term “subject”, refers to an animal, preferably a mammal, and most preferably a human both male and female, who has been the object of treatment, observation or experiment.

The term “therapeutically effective amount” as used herein, means that amount of active compound or pharmaceutical agent that elicits the biological or medicinal response in a tissue system, animal or human that is being sought by a researcher, veterinarian, medical doctor or other clinician, which includes alleviation of one or more of the signs or symptoms of the disease or disorder being treated.

The term “prophylactically effective amount” is intended to mean that amount of a pharmaceutical drug that will prevent or reduce the risk of occurrence of the biological or medical event that is sought to be prevented of a tissue, a system, animal or human that is being sought by a researcher, veterinarian, medical doctor or other clinician.

The term “pharmaceutically acceptable salts or amides” shall mean non-toxic salts or amides of the compounds employed in this invention which are generally prepared by reacting the free acid with a suitable organic or inorganic base. Examples of such salts include, but are not limited to, acetate, benzenesulfonate, benzoate, bicarbonate, bisulfate, bitartrate, borate, bromide, calcium, calcium edetate, camsylate, carbonate, chloride, clavulanate, citrate, dihydrochloride, edetate, edisylate, estolate, esylate, fumarate, gluceptate, gluconate, glutamate, glycollylarsanilate, hexylresorcinate, hydrabamine, hydrobromide, hydrochloride, hydroxynapthoate, iodide, isothionate, lactate, lactobionate, laurate, malate, maleate, mandelate, mesylate, methylbromide, methylnitrate, methylsulfate, mucate, napsylate, nitrate, oleate, oxalate, pamaote, palmitate, panthothenate, phosphate/diphosphate, polygalacturonate, potassium, salicylate, sodium, stearate, subacetate, succinate, tannate, tartrate, teoclate, tosylate, triethiodide, valerate.

Therefore, the term “a patient in need of treatment” as used herein will refer to any subject or patient who currently has or may develop any of the above syndromes or disorders, including any mood disorder which can be treated by antidepressant medication, or any other disorder in which the patient's present clinical condition or prognosis could benefit from the administration of one or more compounds of Formula (1) alone or in combination with another therapeutic intervention including but not limited to another medication.

The term “treating” or “treatment” as used herein, refers to any indicia of success in the prevention or amelioration of an injury, pathology or condition of restless legs syndrome and modification of symptoms of restless legs syndrome, including any objective or subjective parameter such as abatement; remission; diminishing of symptoms or making the injury, pathology, or condition more tolerable to the patient; slowing in the rate of degeneration or decline or worsening of the illness; making the final point of worsening less debilitating; or improving a subject's physical or mental well-being. The treatment or amelioration of symptoms can be based on objective or subjective parameters; including the results of a physical examination, neurological examination, and/or psychiatric evaluations. Accordingly, the term “treating” or “treatment” includes the administration of the compounds or agents of the present invention for treatment of any form of restless legs syndrome in both males and females. In some instances, treatment with the compounds of the present invention will done in combination with other compounds to prevent, inhibit, or arrest the progression of the restless legs syndrome.

The term “therapeutic effect” as used herein, refers to the effective improvement in or reduction of symptoms of restless legs syndrome. The term “a therapeutically effective amount” as used herein means a sufficient amount of one or more of the compounds of the invention to produce a therapeutic effect, as defined above, in a subject or patient in need of such restless legs treatment.

The terms “subject” or “patient” are used herein interchangeably and as used herein mean any mammal including but not limited to human beings including a human patient or subject to which the compositions of the invention can be administered. The term mammals include human patients, both male and female and non-human primates, as well as experimental animals such as rabbits, rats, mice, and other animals.

Methods are known in the art for determining therapeutically and prophylactically effective doses for the instant pharmaceutical composition. For example, the compound can be employed at a daily dose in the range of about 0.1 mg to 400 mg usually on a regimen of several times, for example, 1 to 2 times, per day, for an average adult human. The effective amount, however, may be varied depending upon the particular compound used, the mode of administration, the strength of the preparation, the mode of administration, and the advancement of the disease condition. In addition, factors associated with the particular patient being treated, including patient age, weight, diet and time of administration, will result in the need to adjust dosages.

The compound may be administered to a subject by any conventional route of administration, including, but not limited to, intravenous, oral, subcutaneous, intramuscular, intradermal and parenteral. Depending on the route of administration, compounds of Formula (1) can be constituted into any form. For example, forms suitable for oral administration include solid forms, such as pills, gelcaps, tablets, caplets, capsules (each including immediate release; timed release and sustained release formulations), granules, and powders. Forms suitable for oral administration also include liquid forms, such as solutions, syrups, elixirs, emulsions, and suspensions. In addition, forms useful for parenteral administration include sterile solutions, emulsions and suspensions.

To prepare the pharmaceutical compositions of this invention, one or more compounds of formula (1) or salt thereof as the active ingredient is intimately admixed with a pharmaceutical carrier according to conventional pharmaceutical compounding techniques. Carriers are necessary and inert pharmaceutical excipients, including, but not limited to, binders, suspending agents, lubricants, flavorings, sweeteners; preservatives, dyes, and coatings. In preparing compositions in oral dosage form, any of the usual pharmaceutical carriers may be employed. For example, for liquid oral preparations, suitable carriers and additives include water, glycols, oils, alcohols, flavoring agents, preservatives, coloring agents and the like; for solid oral preparations, suitable carriers and additives include starches, sugars, diluents, granulating agents, lubricants, binders, disintegrating agents and the like. For parenteral use, the carrier will usually comprise sterile water, though other ingredients, for example, for purposes such as aiding solubility or for preservation, may be included. Injectable suspensions may also be prepared, in which case appropriate liquid carriers, suspending agents and the like may be employed.

Because of their ease in administration, tablets and capsules represent the most advantageous oral dosage unit form, in which case solid pharmaceutical carriers are obviously employed. If desired, tablets may be sugar coated or enteric coated by standard techniques. Suppositories may be prepared, in which case cocoa butter could be used as the carrier. The tablets or pills can be coated or otherwise compounded to provide a dosage form affording the advantage of prolonged action. For example, the tablet or pills can comprise an inner dosage and an outer dosage component, the latter being in the form of an envelope over the former. The two components can be separated by an enteric layer, which serves to resist disintegration in the stomach and permits the inner component to pass intact into the duodenum or to be delayed in release. A variety of material can be used for such enteric layers or coatings, such materials including a number of polymeric acids with such materials as shellac, cetyl alcohol and cellulose acetate.

The active drug can also be administered in the form of liposome delivery systems, such as small unilamellar vesicles, large unilamellar vesicles and multilamellar vesicles. Liposomes can be formed from a variety of phospholipids, such as cholesterol, stearylamine or phosphatidylcholines.

Active drug may also be delivered by the use of monoclonal antibodies as individual carriers to which the compound molecules are coupled. Active drug may also be coupled with soluble polymers as targetable drug carriers. Such polymers can include polyvinyl-pyrrolidone, pyran copolymer, polyhydroxy-propyl-methacrylamide-phenol, polyhydroxy-ethyl-aspartamide-phenol, or polyethyleneoxide-polylysine substituted with palmitoyl residues. Furthermore, active drug may be coupled to a class of biodegradable polymers useful in achieving controlled release of a drug, for example, polylactic acid, polyglycolic acid, copolymers of polylactic and polyglycolic acid, polyepsilon caprolactone, polyhydroxy butyric acid, polyorthoesters, polyacetals, polydihydropyrans, polycyanoacrylates and cross linked or amphipathic block copolymers of hydrogels.

Preferably these compositions are in unit dosage forms such as tablets, pills, capsules, powders, granules, sterile parenteral solutions or suspensions, metered aerosol or liquid sprays, drops, ampoules, auto-injector devices or suppositories, for oral parenteral, intranasal, sublingual or rectal administration, or for administration by inhalation or insufflation.

Alternatively, the composition may be presented in a form suitable for once-weekly or once-monthly administration; for example, an insoluble salt of the active compound, such as the decanoate salt, may be adapted to provide a depot preparation for intramuscular injection.

The pharmaceutical compositions herein will contain, per dosage unit, e.g., tablet, capsule, powder, injection, teaspoonful, suppository and the like, an amount of the active ingredient necessary to deliver an effective dose as described above. For example, the pharmaceutical compositions herein can contain, per unit dosage unit, from about 25 to about 400 mg of the active ingredient. Preferably, the range is from about 50 to about 200 mg of the active ingredient.

In some embodiments of the present invention carbamate compounds suitable for use in the practice of this invention will be administered either singly or concomitantly with at least one or more other compounds or therapeutic agents. In these embodiments, the present invention provides methods to treat restless legs syndrome and modification of symptoms associated with restless legs syndrome in a patient. The method includes the step of; administering to a patient in need of treatment, an effective amount of one of the carbamate compounds disclosed herein in combination with an effective amount of one or more other compounds or therapeutic agents.

It is understood that substituents and substitution patterns on the compounds of the present invention can be selected by one of ordinary skill in the art to provide compounds that are chemically stable and that can be readily synthesized by techniques known in the art as well as the methods provided herein.

The present invention includes the use of isolated enantiomers of Formula 1. In one preferred embodiment, a pharmaceutical composition comprising the isolated S-enantiomer of Formula 1 is used to provide restless legs syndrome treatment in a subject. In another preferred embodiment, a pharmaceutical composition comprising the isolated R-enantiomer of Formula 1 is used to provide restless legs syndrome treatment a subject

The present invention also includes the use of mixtures of enantiomers of Formula 1. In one aspect of the present invention, one enantiomer will predominate. An enantiomer that predominates in the mixture is one that is present in the mixture in an amount greater than any of the other enantiomers present in the mixture, e.g., in an amount greater than 50%. In one aspect, one enantiomer will predominate to the extent of 90% or to the extent of 91%, 92%, 93%, 94%, 95%, 96%, 97% or 98% or greater. In one preferred embodiment, the enantiomer that predominates in a composition comprising a compound of Formula 1 is the S-enantiomer of Formula 1.

The present invention provides methods of using enantiomers and enantiomeric mixtures of compounds represented by Formula 1, to treat restless legs syndrome. A carbamate enantiomer of Formula 1 contains an asymmetric chiral carbon at the benzylic position, which is the second aliphatic carbon adjacent to the phenyl ring.

An enantiomer that is isolated is one that is substantially free of the corresponding enantiomer. Thus, an isolated enantiomer refers to a compound that is separated via separation techniques or prepared free of the corresponding enantiomer. The term “substantially free,” as used herein, means that the compound is made up of a significantly greater proportion of one enantiomer. In preferred embodiments, the compound includes at least about 90% by weight of a preferred enantiomer. In .other embodiments of the invention, the compound includes at least about 99% by weight of a preferred enantiomer. Preferred enantiomers can be isolated from racemic mixtures by any method known to those skilled in the art, including high performance liquid chromatography (HPLC) and the formation and crystallization of chiral salts, or preferred enantiomers can be prepared by methods described herein.

Carbamate Compounds as Pharmaceuticals:

The present invention provides racemic mixtures, enantiomeric mixtures and isolated enantiomers of Formula 1 as pharmaceuticals. The carbamate compounds are formulated as pharmaceuticals to provide anti-restless legs syndrome action in a subject.

In general, the carbamate compounds of the present invention can be administered as pharmaceutical compositions by any method known in the art for administering therapeutic drugs including oral, buccal, topical, systemic (e.g., transdermal, intranasal, or by suppository), or parenteral (e.g., intramuscular, subcutaneous, or intravenous injection.) Administration of the compounds directly to the nervous system can include, for example, administration to intracerebral, intraventricular, intacerebroventricular, intrathecal, intracisternal, intraspinal or peri-spinal routes of administration by delivery via intracranial or intravertebral needles or catheters with or without pump devices.

Compositions can take the form of tablets, pills, capsules, semisolids, powders, sustained release formulations, solutions, suspensions, emulsions, syrups, elixirs, aerosols, or any other appropriate compositions; and comprise at least one compound of this invention in combination with at least one pharmaceutically acceptable excipient. Suitable excipients are well known to persons of ordinary skill in the art, and they, and the methods of formulating the compositions, can be found in such standard references as Alfonso AR: Remington's Pharmaceutical Sciences, 17th ed., Mack Publishing Company, Easton Pa., 1985, the disclosure of which is incorporated herein by reference in its entirety and for all purposes. Suitable liquid carriers, especially for injectable solutions, include water, aqueous saline solution, aqueous dextrose solution, and glycols.

The carbamate compounds can be provided as aqueous suspensions. Aqueous suspensions of the invention can contain a carbamate compound in admixture with excipients suitable for the manufacture of aqueous suspensions. Such excipients can include, for example, a suspending agent, such as sodium carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, sodium alginate, polyvinylpyrrolidone, gum tragacanth and gum acacia, and dispersing or wetting agents such as a naturally occurring phosphatide (e.g., lecithin), a condensation product of an alkylene oxide with a fatty acid (e.g., polyoxyethylene stearate), a condensation product of ethylene oxide with a long chain aliphatic alcohol (e.g., heptadecaethylene oxycetanol), a condensation product of ethylene oxide with a partial ester derived from a fatty acid and a hexitol (e.g., polyoxyethylene sorbitol mono-oleate), or a condensation product of ethylene oxide with a partial ester derived from fatty acid and a hexitol anhydride (e.g., polyoxyethylene sorbitan mono-oleate).

The aqueous suspension can also contain one or more preservatives such as ethyl or n-propyl p-hydroxybenzoate, one or more coloring agents, one or more flavoring agents, and one or more sweetening agents, such as sucrose, aspartame or saccharin. Formulations can be adjusted for osmolarity.

Oil suspensions for use in the present methods can be formulated by suspending a carbamate compound in a vegetable oil, such as arachis oil, olive oil, sesame oil or coconut oil, or in a mineral oil such as liquid paraffin; or a mixture of these. The oil suspensions can contain a thickening agent, such as beeswax, hard paraffin or cetyl alcohol. Sweetening agents can be added to provide a palatable oral preparation, such as glycerol, sorbitol or sucrose. These formulations can be preserved by the addition of an antioxidant such as ascorbic acid. As an example of an injectable oil vehicle, see Minto, J. Pharmacol. Exp. Ther. 281:93-102, 1997. The pharmaceutical formulations of the invention can also be in the form of oil-in-water emulsions. The oily phase can be a vegetable oil or a mineral oil, described above, or a mixture of these.

Suitable emulsifying agents include naturally occurring gums, such as gum acacia and gum tragacanth, naturally occurring phosphatides, such as soybean lecithin, esters or partial esters derived from fatty acids and hexitol anhydrides, such as sorbitan mono-oleate, and condensation products of these partial esters with ethylene oxide, such as polyoxyethylene sorbitan mono-oleate. The emulsion can also contain sweetening agents and flavoring agents, as in the formulation of syrups and elixirs. Such formulations can also contain a demulcent, a preservative, or a coloring agent.

The compound of choice, alone or in combination with other suitable components can be made into aerosol formulations (i.e., they can be “nebulized”) to be administered via inhalation. Aerosol formulations can be placed into pressurized acceptable propellants, such as dichlorodifluoromethane, propane, nitrogen, and the like.

Formulations of the present invention suitable for parenteral administration, such as, for example, by intraarticular (in the joints), intravenous, intramuscular, intradermal, intraperitoneal, and subcutaneous routes, can include aqueous and non-aqueous, isotonic sterile injection solutions, which can contain antioxidants, buffers, bacteriostats, and solutes that render the formulation isotonic with the blood of the intended recipient, and aqueous and non-aqueous sterile suspensions that can include suspending agents, solubilizers, thickening agents, stabilizers, and preservatives. Among the acceptable vehicles and solvents that can be employed are water and Ringer's solution, an isotonic sodium chloride. In addition, sterile fixed oils can conventionally be employed as a solvent or suspending medium. For this purpose, any bland fixed oil can be employed including synthetic mono- or diglycerides. In addition, fatty acids such as oleic acid can likewise be used in the preparation of injectables. These solutions are sterile and generally free of undesirable matter.

Where the compounds are sufficiently soluble they can be dissolved directly in normal saline with or without the use of suitable organic solvents, such as propylene glycol or polyethylene glycol. Dispersions of the finely divided compounds can be made-up in aqueous starch or sodium carboxymethyl cellulose solution, or in suitable oil, such as arachis oil. These formulations can be sterilized by conventional, well-known sterilization techniques. The formulations can contain pharmaceutically acceptable auxiliary substances as required to approximate physiological conditions such as pH adjusting and buffering agents, toxicity adjusting agents, e.g., sodium acetate, sodium chloride, potassium chloride, calcium chloride, sodium lactate and the like.

The concentration of a carbamate compound in these formulations can vary widely, and will be selected primarily based on fluid volumes, viscosities, body weight, and the like, in accordance with the particular mode of administration selected and the patient's needs. For IV administration, the formulation can be a sterile injectable preparation, such as a sterile injectable aqueous or oleaginous suspension. This suspension can be formulated according to the known art using those suitable dispersing or wetting agents and suspending agents. The sterile injectable preparation can also be a sterile injectable solution or suspension in a nontoxic parenterally acceptable diluents or solvent, such as a solution of 1,3-butanediol. The formulations of commends can be presented in unit-dose or multi-dose sealed containers, such as ampoules and vials. Injection solutions and suspensions can be prepared from sterile powders, granules, and tablets of the kind previously described.

A carbamate compound suitable for use in the practice of this invention can be and is preferably administered orally. The amount of a compound of the present invention in the composition can vary widely depending on the type of composition, size of a unit dosage, kind of excipients, and other factors well known to those of ordinary skill in the art. In general, the final composition can comprise, for example, from 0.000001 percent by weight (% w) to 50% w of the carbamate compound, preferably 0.00001% w to 25% w, with the remainder being the excipient or excipients.

Pharmaceutical formulations for oral administration can be formulated using pharmaceutically acceptable carriers well known in the art in dosages suitable for oral administration. Such carriers enable the pharmaceutical formulations to be formulated in unit dosage forms as tablets, pills, powder, dragees, capsules, liquids, lozenges, gels, syrups, slurries, suspensions, etc. suitable for ingestion by the patient.

Formulations suitable for oral administration can consist of (a) liquid solution, such as an effective amount of the pharmaceutical formulation suspended in a diluents, such as water, saline or polyethyleneglycol (PEG) 400; (b) capsules, sachets or tablets, each containing a predetermined amount of the active ingredient, as liquids, solids, granules or gelatin; (c) suspensions in an appropriate liquid; and (d) suitable emulsions.

Pharmaceutical preparations for oral use can be obtained through combination of the compounds of the present invention with a solid excipient, optionally grinding a resulting mixture, and processing the mixture of granules, after adding suitable additional compounds, if desired, to obtain tablets or dragee cores. Suitable solid excipients are carbohydrate or protein fillers and include, but are not limited to sugars, including lactose, sucrose, mannitol, or sorbitol; starch from corn, wheat, rice, potato, or other plants; cellulose such as methyl cellulose, hydroxymethyl cellulose, hydroxypropylmethyl-cellulose or sodium carboxymethylcellulose; and gums including arabic and tragacanth; as well as proteins such as gelatin and collagen.

If desired, disintegrating or solubilizing agents can be added, such as the cross-linked polyvinyl pyrrolidone, agar, alginic acid, or a salt thereof, such as sodium alginate. Tablet forms can include one or more of lactose, sucrose, mannitol, sorbitol, calcium phosphates, corn starch, potato starch, microcrystalline cellulose, gelatin, colloidal silicon dioxide, talc, magnesium stearate, stearic acid, and other excipients, colorants, fillers, binders, diluents, buffering agents, moistening agents, preservatives, flavoring agents, dyes, disintegrating agents, and pharmaceutically compatible carriers. Lozenge forms can comprise the active ingredient in a flavor, e.g., sucrose, as well as pastilles comprising the active ingredient in an inert base, such as gelatin and glycerin or sucrose and acacia emulsions, gels, and the like containing, in addition to the active ingredient, carriers known in the art.

The compounds of the present invention can also be administered in the form of suppositories for rectal administration of the drug. These formulations can be prepared by mixing the drug with a suitable non-irritating excipient that is solid at ordinary temperatures but liquid at the rectal temperatures and will therefore melt in the rectum to release the drug. Such materials are cocoa butter and polyethylene glycols.

The compounds of the present invention can also be administered by intranasal, intraocular, intravaginal, and intrarectal routes including suppositories, insufflation, powders and aerosol formulations (for examples of steroid inhalants, see Rohatagi, J. Clin. Pharmacol. 35:1187-1193, 1995; Tjwa, Ann. Allergy Asthma Immunol. 75:107-111, 1995).

The compounds of the present invention can be delivered transdermally, by a topical route, formulated as applicator sticks, solutions, suspensions, emulsions, gels, creams, ointments, pastes, jellies, paints, powders, and aerosols.

Encapsulating materials can also be employed with the compounds of the present invention and the term “composition” can include the active ingredient in combination with an encapsulating material as a formulation, with or without other carriers. For example, the compounds of the present invention can also be delivered as microspheres for slow release in the body. In one embodiment, microspheres can be administered via intradermal injection of drug (e.g., mifepristone)-containing microspheres, which slowly release subcutaneously (see Rao, J. Biomater Sci. Polym. Ed. 7:623-645, 1995; as biodegradable and injectable gel formulations (see, e.g., Gao, Pharm. Res. 12:857-863, 1995); or, as microspheres for oral administration (see, e.g., Eyles, J. Pharm. Pharmacol. 49:669-674, 1997). Both transdermal and intradermal routes afford constant delivery for weeks or months. Cachets can also be used in the delivery of the compounds of the present invention.

In another embodiment, the compounds of the present invention can be delivered by the use of liposomes which fuse with the cellular membrane or are endocytosed, i.e., by employing ligands attached to the liposome that bind to surface membrane protein receptors of the cell resulting in endocytosis. By using liposomes, particularly where the liposome surface carries ligands specific for target cells, or are otherwise preferentially directed to a specific organ, one can focus the delivery of the carbamate compound into target cells in vivo. (See, e.g., Al-Muhammed, J. Microencapsul. 13:293-306, 1996; Chonn, Curr. Opin. Biotechnol. 6:698-708, 1995; Ostro, Am. J. Hosp. Pharm. 46:1576-1587, 1989).

The pharmaceutical formulations of the invention can be provided as a salt and can be formed with many acids, including but not limited to hydrochloric, sulfuric, acetic, lactic, tartaric, malic, succinic, etc. Salts tend to be more soluble in aqueous or other protonic solvents that are the corresponding free base forms. In other cases, the preferred preparation can be a lyophilized powder which can contain, for example, any or all of the following: 1 mM-50 mM histidine, 0.1%-2% sucrose, 2%-7% mannitol, at a pH range of 4.5 to 5.5, that is combined with buffer prior to use.

Pharmaceutically acceptable salts refer to salts that are pharmaceutically acceptable and have the desired pharmacological properties. Such salts include salts that may be formed where acidic protons present in the compounds are capable of reacting with inorganic or organic bases. Suitable inorganic salts include those formed with the alkali metals, e.g. sodium and potassium, magnesium, calcium, and aluminum. Suitable organic salts include those formed with organic bases such as the amine bases, e.g. ethanolamine, diethanolamine, triethanolamine, tromethamine, N methylglucamine, and the like. Pharmaceutically acceptable salts can also include acid addition salts formed from the reaction of amine moieties in the parent compound with inorganic acids (e.g. hydrochloric and hydrobromic acids) and organic acids (e.g. acetic acid, citric acid, maleic acid, and the alkane- and arene-sulfonic acids such as methanesulfonic acid and benzenesulfonic acid). Pharmaceutically acceptable esters include esters formed from carboxy, sulfonyloxy, and phosphonoxy groups present in the compounds. When there are two acidic groups present, a pharmaceutically acceptable salt or ester may be a mono-acid-mono-salt or ester or a di-salt or ester; and similarly where there are more than two acidic groups present, some or all of such groups can be salified or esterified.

Compounds named in this invention can be present in unsalified or unesterified form, or in salified and/or esterified form, and the naming of such compounds is intended to include both the original (unsalified and unesterified) compound and its pharmaceutically acceptable salts and esters. The present invention includes pharmaceutically acceptable salt and ester forms of Formula (1). More than one crystal form of an enantiomer of Formula 1 can exist and as such are also included in the present invention.

A pharmaceutical composition of the invention can optionally contain, in addition to a carbamate compound, at least one other therapeutic agent useful in the treatment of restless legs syndrome. For example, the carbamate compounds of Formula 1 can be combined physically with other restless legs syndrome treatments in fixed dose combinations to simplify their administration.

Methods of formulating pharmaceutical compositions have been described in numerous publications such as Pharmaceutical Dosage Forms: Tablets. Second Edition. Revised and Expanded. Volumes 1-3, edited by Lieberman et al; Pharmaceutical Dosage Forms: Parenteral Medications. Volumes 1-2, edited by Avis et al; and Pharmaceutical Dosage Forms: Disperse Systems. Volumes 1-2, edited by Lieberman et al; published by Marcel Dekker, Inc, the disclosure of which are herein incorporated by reference in their entireties and for all purposes.

The pharmaceutical compositions are generally formulated as sterile, substantially isotonic and in full compliance with all Good Manufacturing Practice (GMP) regulations of the U.S. Food and Drug Administration.

Dosage Regimens

The present invention provides methods of providing anti-restless legs syndrome action in a mammal using carbamate compounds. The amount of the carbamate compound necessary to reduce or treat restless legs syndrome is defined as a therapeutically or a pharmaceutically effective dose. The dosage schedule and amounts effective for this use, i.e., the dosing or dosage regimen will depend on a variety of factors including the stage of the disease, the patient's physical status, age and the like. In calculating the dosage regimen for a patient, the mode of administration is also taken into account.

A person of ordinary skill in the art will be able without undue experimentation, having regard to that skill and this disclosure, to determine a therapeutically effective amount of a particular substituted carbamate compound for practice of this invention (see, e.g., Lieberman, Pharmaceutical Dosage Forms (Vols. 1-3, 1992); Lloyd, 1999, The art, Science and Technology of Pharmaceutical Compounding; and Pickar, 1999, Dosage Calculations). A therapeutically effective dose is also one in which any toxic or detrimental side effects of the active agent that is outweighed in clinical terms by therapeutically beneficial effects. It is to be further noted that for each particular subject, specific dosage regimens should be evaluated and adjusted over time according to the individual need and professional judgment of the person administering or supervising the administration of the compounds.

For treatment purposes, the compositions or compounds disclosed herein can be administered to the subject in a single bolus delivery, via continuous delivery over an extended time period, or in a repeated administration protocol (e.g., by an hourly, daily or weekly, repeated administration protocol). The pharmaceutical formulations of the present invention can be administered, for example, one or more times daily, 3 times per week, or weekly. In one embodiment of the present invention, the pharmaceutical formulations of the present invention are orally administered once or twice daily.

In this context, a therapeutically effective dosage of the carbamate compounds can include repeated doses within a prolonged treatment regimen that will yield clinically significant results to treat restless legs syndrome. Determination of effective dosages in this context is typically based on animal model studies followed up by human clinical trials and is guided by determining effective dosages and administration protocols that significantly reduce the occurrence or severity of targeted exposure symptoms or conditions in the subject. Suitable models in this regard include, for example, murine, rat, porcine, feline, non-human primate, and other accepted animal model subjects known in the art. Alternatively, effective dosages can be determined using in vitro models (e.g., immunologic and histopathologic assays). Using such models, only ordinary calculations and adjustments are typically required to determine an appropriate concentration and dose to administer a therapeutically effective amount of the biologically active agent(s) (e.g., amounts that are intranasally effective, transdermally effective, intravenously effective, or intramuscularly effective to elicit a desired response).

In an exemplary embodiment of the present invention, unit dosage forms of the compounds are prepared for standard administration regimens. In this way, the composition can be subdivided readily into smaller doses at the physician's direction. For example, unit dosages can be made up in packeted powders, vials or ampoules and preferably in capsule or tablet form.

The active compound present in these unit dosage forms of the composition can be present in an amount of, for example, from about 10 mg to about one gram or more, for single or multiple daily administration, according to the particular need of the patient. By initiating the treatment regimen with a minimal daily dose of about one gram, the blood levels of the carbamate compounds can be used to determine whether a larger or smaller dose is indicated.

Effective administration of the carbamate compounds of this invention can be administered, for example, at an oral or parenteral dose of from about 0.01 mg/kg/dose to about 150 mg/kg/dose. Preferably, administration will be from about 0.1 mg/kg/dose to about 25 mg/kg/dose, more preferably from about 0.2 to about 18 mg/kg/dose. Therefore, the therapeutically effective amount of the active ingredient contained per dosage unit as described herein can be, for example, from about 1 mg/day to about 7000 mg/day for a subject having, for example, an average weight of 70 kg.

The methods of this invention also provide for kits for use in providing treatment of restless legs syndrome. After a pharmaceutical composition comprising one or more carbamate compounds of this invention, with the possible addition of one or more other compounds of therapeutic benefit, has been formulated in a suitable carrier, it can be placed in an appropriate container and labeled for providing restless legs syndrome treatment. Additionally, another pharmaceutical comprising at least one other therapeutic agent useful in the restless legs syndrome treatment can be placed in the container as well and labeled for treatment of the indicated disease. Such labeling can include, for example, instructions concerning the amount, frequency and method of administration of each pharmaceutical.

Although the foregoing invention has been described in detail by way of example for purposes of clarity of understanding, it will be apparent to the artisan that certain changes and modifications are comprehended by the disclosure and may be practiced without undue experimentation within the scope of the appended claims, which are presented by way of illustration not limitation. The following examples are provided to illustrate specific aspects of the invention and are not meant to be limitations.

A better understanding of the present invention may be obtained in light of the following examples that are set forth to illustrate, but are not to be construed to limit, the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the influence of the tested compound on spontaneous activity (distance traveled) in mice.

EXAMPLE 1

O-carbamoyl-(D)-phenylalaninol (hereinafter, referred to test compound) was tested for binding to the dopamine, norepinephrine and serotonin transporters and for the effects on dopamine, norepinephrine and serotonin reuptake. The test compound showed weak binding to the dopamine and norepinephrine transporter and weak effects on dopamine and norepinephrine reuptake compared to cocaine.

(Methods)

Compounds to be tested were weighed and dissolved in DMSO (dimethyl sulfoxide) to make a 10 or 100 mM stock solution. An initial dilution to 50 or 500 μM in assay buffer for binding, or to 1 or 10 mM in assay buffer for uptake, was made. Subsequent dilutions were made with assay buffer supplemented with DMSO, maintaining a final concentration of 0.1% DMSO. Pipetting was conducted using a Biomek 2000 robotic workstation. The concentrations of the test compounds are shown in following Table 1.

TABLE 1 Concentrations of Test Compound tested Concentration Assay Range Binding hDAT (human dopamine transporter) 21.6 nM-100 μM hSERT (human serotonin transporter) 21.6 nM-100 μM hNET (human norepinephrine transporter) 21.6 nM-10 μM Uptake hDAT (human dopamine transporter) 31.6 nM-10 μM hSERT (human serotonin transporter) 31.6 nM-100 μM hNET (human norepinephrine transporter) 31.6 nM-100 μM

Inhibition of Radioligand Binding of [¹²⁵I]RTI-55 to hDAT, hSERT or hNET in Clonal Cells:

Cell preparation: HEK293 cells (American Type Culture Collection, ATCC) expressing hDAT, hSERT or hNET inserts are grown to 80% confluence on 150 mm diameter tissue culture dishes dishes in a humidified 10% CO₂ environment at 37° C. and served as the tissue source. HEK-hDAT and HEK-hSERT cells were incubated in Dulbecco's modified Eagle's medium supplemented with 5% fetal bovine serum, 5% calf bovine serum, 0.05 U penicillin/streptomycin and puromycin (2 μg/mL). HEK-hNET cells were incubated in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum, 0.05 U penicillin/streptomycin and geneticin (300 μg/mL). Cell membranes are prepared as follows. Medium is poured off the plate, and the plate is washed with 10 ml of calcium- and magnesium-free phosphate-buffered saline. Lysis buffer (10 ml; 2 mM HEPES with 1 mM EDTA) is added. After 10 min, cells are scraped from plates, poured into centrifuge tubes, and centrifuged 30,000×g for 20 min. The supernatant fluid is removed, and the pellet is resuspended in 12-32 ml of 0.32 M sucrose using a Polytron at setting 7 for 10 sec. The resuspension volume depends on the density of binding sites within a cell line and is chosen to reflect binding of 10% or less of the total radioactivity.

Assay conditions: Each assay tube contains 50 μl of membrane preparation (about 10-15 μg of protein; described above), 25 μl of test compound, compound used to define non-specific binding (mazindol or imipramine), and/or buffer (Krebs-HEPES, pH 7.4; 122 mM NaCl, 2.5 mM CaCl2, 1.2 mM MgSO4, 10 μM pargyline, 100 μM tropolone, 0.2% glucose and 0.02% ascorbic acid, buffered with 25 mM HEPES, 25 pl of [¹²⁵I]RTI-55 ((−)-2β-Carbomethoxy-3β-(4-iodophenyl)tropane, iometopane; 40-80 μM final concentration) and additional buffer (Krebs-HEPES) sufficient to bring up the final volume to 250 μl. Membranes are preincubated with test compound for 10 min at 25° C. prior to the addition of the [¹²⁵O]RTI-55. The assay tubes are incubated at 25° C. for 90 min. Binding is terminated by filtration over GF/C filters using a Tomtec 96-well cell harvester. Filters are washed for six seconds with ice-cold saline. Scintillation fluid is added to each square and radioactivity remaining on the filter is determined using a Wallac p- or beta-plate reader. Specific binding is defined as the difference in binding observed in the presence and absence of 5 μM mazindol (HEK-hDAT and HEK-hNET) or 5 μM imipramine (HEK-hSERT). Two or three independent competition experiments are conducted with duplicate determinations. GraphPAD Prism is used to analyze the ensuing data, with IC₅₀ values converted to K_(i) values using the Cheng-Prusoff equation (K_(i)=IC₅₀/(1+([RTI-55]/K_(d)RTI-55))).

Filtration Assay for Inhibition of [³H]Neurotransmitter Uptake in HEK293 Cells Expressing Recombinant Biogenic Amine Transporters:

Cell preparation: Cells are grown to confluence as described above. The medium is removed, and cells are washed twice with phosphate buffered saline (PBS) at room temperature. Following the addition of 3 ml Krebs-HEPES buffer (preparation described above) the plates are warmed in a 25° C. water bath for 5 min. The cells are gently scraped and then triturated with a pipette. Cells from multiple plates are combined. One plate provides enough cells for 48 wells, which is required to generate data on two complete curves for the test compounds.

Uptake inhibition assay conditions: The assay is conducted in 96 1-ml vials. Krebs-HEPES (350 μl) and test compounds, compounds used to define non-specific uptake, or buffer (50 μl) are added to vials and placed in a 25° C. water bath. Specific uptake is defined as the difference in uptake observed in the presence and absence of 5 μM mazindol (HEK-hDAT and HEK-hNET) or 5 μM imipramine (HEK-hSERT). Cells (50 μl) are added and preincubated with the test compounds for 10 min. The assay is initiated by the addition of [³H]dopamine, [³H]serotonin, or [³H]norepinephrine (50 μl, 20 nM final concentration). Filtration through Whatman GF/C filters presoaked in 0.05% (w/v) polyethylenimine is used to terminate uptake after 10 min. The IC₅₀s are calculated applying the GraphPAD Prism program to triplicate curves made up of 6 drug concentrations each. Two or three independent determinations of each curve are made.

(Results)

The test compound was tested for its effects on radioligand ([¹²⁵I]RTI-55) binding to and [³H]dopamine uptake by HEK cells expressing eDNA for the human dopamine transporter (HEK-hDAT cells), its effects on radioligand ([¹²⁵I]RTI-55) binding and [³H]serotonin uptake by HEK cells expressing eDNA for the human serotonin transporter (HEK-hSERT cells), and its effects on radioligand ([¹²⁵I]RTI-55) binding and [³H]norepinephrine uptake by HEK cells expressing eDNA for the human norepinephrine transporter (HEK-hNET cells).

In HEK-hDAT cells, the affinity of the compound for the binding site was lower than the affinity of cocaine, the standard compound, for the same site(s). The K_(i) value for the displacement of [¹²⁵I]RTI-55 by the test compound was 14,200 nM, and the K_(i) value for cocaine displacement of [¹²⁵I]RTI-55 binding was 236 nM. In the uptake assays test compound was less potent at blocking the uptake of [³H]dopamine, with an IC₅₀ value of 2900 nM, as compared to the potency of cocaine (IC₅₀=385 nM). A Hill coefficient other than one suggests complex interactions with binding or uptake sites.

In HEK-hSERT cells, the affinity of the compound for the binding site was lower than the affinity of cocaine, the standard compound, for the same site(s). The K_(i) value for the displacement of [¹²⁵I]RTI-55 by test compound was 81,500 nM, and the K_(i) value for cocaine displacement of [¹²⁵I]RTI-55 binding was 361 nM. In the uptake assays 31,827 was less potent at blocking the uptake of [3H]serotonin, with an IC₅₀ value greater than 100 μM, as compared to the potency of cocaine (IC₅₀=355 nM).

In HEK-hNET cells, the affinity of the compound for the binding site was lower than the affinity of cocaine, the standard compound, for the same site(s). The K_(i) value for the displacement of [¹²⁵I]RTI-55 test compound was 3700 nM, and the K_(i) value for cocaine displacement of [¹²⁵I]RTI-55 binding was 505 nM. In the uptake assays test compound was less potent at blocking the uptake of [³H]norepinephrine, with an IC₅₀ value of 4400 nM, as compared to the potency of cocaine (IC₅₀=194 nM).

The obtained results are shown in following Table 2:

TABLE 2 Effects of test compound on HEK-hDAT, HEK-hSERT and HEK- hNET cells Test Compound Cocaine HEK-hDAT cells [¹²⁵I]RTI-55 Binding K_(i) (nM) 14,200 ± 3,500 236 ± 58 Hill coefficient −0.77 ± 0.12 −0.83 ± 0.04 [³H]Dopamine Uptake IC₅₀ (nM) 2900 ± 920 385 ± 54 HEK-hSERT cells [¹²⁵I]RTI-55 Binding K_(i) (nM) 81,500 ± 2,900 361 ± 65 Hill coefficient −2.28 ± 0.05 −0.77 ± 0.04 [³H]Serotonin Uptake IC₅₀ (nM) >100 μM 355 ± 39 HEK-hNET cells [¹²⁵I]RTI-55 Binding K_(i) (nM)  3700 ± 1000 505 ± 67 Hill coefficient −1.45 ± 0.34 −0.67 ± 0.07 [³H]NE Uptake IC₅₀ (nM)  4400 ± 1100 194 ± 29

Numbers represent the means±SEM from at least three independent experiments, each conducted with duplicate (for binding assays) or triplicate (for uptake assays) determinations. When the K_(i) or the IC₅₀ for the test compound is greater than 10 μM, only two experiments are conducted and no standard error is reported.

EXAMPLE 2

The test compound administered at 10, 30 and 100 mg/kg subcutaneously (SC) was assessed to determine the influence on spontaneous activity of wild-type and homozygous mutant dopamine transporter knockout (KO) mice. The test compound selectively reduced activity of the KO mice in a dose-dependent manner suggesting that the test compound was highly efficacious in depressing hyper motor activity in dopamine transporter KO mice.

(Methods)

Male and female wild-type and homozygous mutant dopamine transporter KO mice (n˜10 mice/genotype/agent; produced by in vivo homologous recombination and bred at Duke University Medical Center, Durham, N.C.) were tested for spontaneous activity in the open field following a single injection of the vehicle or compound. Mice were placed into the open field for 30 min and administered SC the vehicle (sterile water), 2 mg/kg amphetamine, or three concentrations of the test compound (10, 30, 100 mg/kg). All drugs were given in a volume of 5 mL/kg. Animals were returned to the open field for an additional 90 min. Spontaneous activity was evaluated in an automated Omnitech Digiscan apparatus (Accuscan Instruments, Columbus, Ohio). Activity was summated at 5 min intervals over the 2 h period of testing. Horizontal activity or locomotion was measured in terms of the total distance covered in cm, vertical activity or rearing was expressed in terms of the total numbers of vertical beam breaks, and stereotypy was quantified in terms of repetitive breaks of a given beam or beams with intervals of less than 1 sec. For the analyses, 10 WT and 10 KO mice were run in each of the treatment groups with approximately equal numbers of males and females assigned to each group. Data were analyzed by the Statistical Package for Social Sciences programs (version 11.0 for Windows; SPSS Science, Chicago, Ill.). The results for each dependent variable were analyzed by repeated analyses of variance (RMANOVA) for within subjects effects (group differences over time) and between-subjects effects (tests of main effects and interactions). Bonferroni corrected pair-wise comparisons were used as the post-hoc tests. A p<0.05 was considered significant.

(Results)

Baseline: KO mice showed higher levels of locomotor, rearing and stereotypical activities compared to WT mice.

Drug Treatment: Amphetamine (AMPH) at 2 mg/kg SC increased locomotor, rearing and stereotypical activities in WT mice and decreased them in KO animals relative to the respective vehicle controls. The test compound reduced activities in a dose-dependent fashion and the 100 mg/kg dose suppressed activities more efficiently than amphetamine. Please see representative Figure below for the locomotor activity (distance traveled in cm) collapsed over the 90 min post-injection period for Amphetamine (AMPH) and test compound. Rearing and stereotyped behavior showed similar results.

The obtained results are shown in FIG. 1.

EXAMPLE 3

The test compound (0-carbamoyl-(D)-phenylalaninol) administered at 30 mg/kg intraperitoneally (IP) significantly increased paw withdrawal latency to a thermal stimulus in rats with sciatic nerve ligation. These data suggest that the test compound shows anti-thermal hyperalgesic properties.

(Methods)

Young adult male Sprague-Dawley rats (CD(SD)IGS, 150-200 g) were initially anesthetized with isoflurane in O₂ by a mask and the surgical procedure was performed according to the method described by Bennett and Xie (1988). Briefly, the right sciatic nerves were loosely tied using ligatures. All experiments were conducted in accordance with the guidelines of the International Association for the Study of Pain. The behavioral tests were conducted at least 14 days postoperatively.

The test compound was dissolved in saline and administered intraperitoneally at 30 mg/kg to animals in a volume of 3 mL/kg body weight.

To test for thermal hyperalgesia, the thermal response was determined by the hindpaw withdrawal latency, using a plantar tester (UGO BASILE, Italy), and a modified method of Hargreaves et al. (1988). Rats were allowed to acclimate within plastic enclosures on a clear glass plate maintained at room temperature. A radiant heat source (intensity 90) was controlled with a timer and focused onto the plantar surface of the rat right hind paw encompassing the glabrous skin. Paw withdrawal stopped both heat source and timer. A maximal cut-off 30 sec was used to prevent tissue damage. Rats were assessed for thermal hyperalgesia predose (0 hr) and at 1, 4 and 8 hours after 30 mg/kg test compound administration.

Data are expressed as mean±standard error of mean (SEM). The values of behavioral signs of neuropathic pain at various postoperative time points were compared with those of the preoperative control period by a repeated-measure One-way Analysis of Variance (followed by Dunnett's post-hoc test). P-values less than 0.05 were considered to be significant.

(Results)

The anti-heat hyperalgesic effects of test compound in the nerve-injured rats are displayed in Table 2 below. The test compound, administered intraperitoneally to rats, significantly increased the paw withdrawal latency to noxious thermal stimuli in comparison with the pre-injection (0 hr) withdrawal latency at 30 mg/kg, IP. The obtained results are shown in following Table 3.

TABLE 3 Anti-thermal hyperalgesic effects (mean paw withdrawal latency in seconds) of the test compound Drug Dose Time Post-Injection (mg/kg, IP) 0 hr 1 hr 4 hr 8 hr Test 5.17 ± 0.27 6.33 ± 0.14** 6.06 ± 0.21* 5.63 ± 0.16 Compound (22.3%^(@)) (17.2%) (8.8%) (30, n = 6) Data are expressed as mean paw withdrawal latency (sec) ± SEM *P < 0.05, **P < 0.01 vs. Paw withdrawal latency (sec) at 0 hr ^(@)% of Antagonism: [((Paw withdrawal latency (sec) at each time point/Paw withdrawal latency (sec) at 0 hr) − 1)] × 100

EXAMPLE 4

The effects of the test compound (50-150 mg/kg, PO on various sleep parameters were evaluated in 8 hypocretin cell ablated narcoleptic mice (prepororexin/ataxin-3 transgenic) and their littermate wild-type mice, and the effects were compared with those of modafinil, a reference wake-promoting compound. The test compound showed significantly increased bouts of wakefulness in both wild-type and narcoleptic mice and was able to normalize sleep patterns of narcoleptic mice.

(Methods)

The polygraph signal (EEG (electroencephalography) and EMG (electromyography)) was captured with SleepSign (Kissei Comtech), and the sleep stage was visually scored with 10 sec epoch for wakefulness, non-REM sleep and REM sleep. Scoring criteria are: Wakefulness is characterized by desynchronized low-amplitude, mixed frequency (>4 Hz) EEG and high EMG activity. Rhythmic alpha (8-9 Hz) wave (with high EMG activities) may also appear. Non-REM is characterized by synchronized, high-amplitude, low-frequency (0.25-4 Hz) with reduced EMG activity (compared to wakefulness). EEG activity in REM sleep is similar to that in wakefulness, with desynchronized, mixed frequency low amplitude waves. Rhythmic alpha (8-9 Hz) wave with reduced EMG activities may also appear. EEG activity during REM sleep is reduced even further and in many cases, completely absent. Some muscle twitching may be apparent in the EMG trace during REM sleep.

Three drug doses of the test compound (50, 100 and 150 mg/kg PO) plus vehicle, was orally administered at ZT 2 (Zeitgeber time: 2 hours after light on) or ZT14 (Zeitgeber time: 2 hours after light off) and the effects on sleep was monitored for 6 hours after the drug administration (the sleep data was collected for 30 hours after the drug injection, and are available for further analysis). The doses for modafinil were 50 and 200 mg/kg PO (plus vehicle), and modafinil was also administered at ZT 2 and ZT 14.

If the polygraph signals of some mice were not sufficient to score the sleep stage with accuracy (especially bad EMG), data from these animals were excluded, and the minimum of 5 animals (except for the highest dose of the test compound in wild-type mice in dark period, n=4) were included for the data analysis and number of animals were indicated in the figures.

Effects of test compound and modafinil on the amount of wake, non-REM sleep, REM sleep (cumulative seconds), number of episodes for each sleep stage during 6 hours, mean wake/sleep-bout lengths (seconds) were analyzed in each animal and the mean of each parameter was calculated in each genotype. The effects of compounds on wake and sleep amounts are useful to evaluate the wake promoting potency, and the number of episodes for each sleep stage and the mean wake/sleep bout length are parameters for evaluating the sleep fragmentation. Amphetamine and modafinil, two main wake-promoting compounds currently used for the treatment of EDS associated with various etiologies (narcolepsy, idiopathic hypersomnia and secondary EDS), are known to increase wake time and prolong wake bout length in normal and EDS conditions.

With these data analyses, the wake-promoting and therapeutic effects of test compound in narcolepsy were evaluated, and the effects were compared with those of modafinil. A comparison of the effects between hypocretin deficient and wild-type mice is very useful in determining if the wake-promotion of the test compound is dependent on the availability of hypocretins, and if there is a possible change in the sensitivity of the receptive mechanisms of test compound in narcoleptic mice due to the hypocretin ligand deficiency.

(Results)

Effects on Sleep During the Resting Period:

Very potent wake-promoting effects of test compound in both wild-type and hypocretin-deficient narcoleptic mice were observed. The effects were dose-dependent, and administrations of 50, 100, 150 mg/kg PO of test compound induced continuous wakefulness in most wild-type and narcoleptic mice for up to 3, 4 and 5 hours, respectively. During this period, Non-REM and REM sleep were completely suppressed. There were no abnormal EEG patterns after test compound administration, and sleep that occurred after the prolonged wakefulness was normal by polygraphic assessments.

In contrast, the wake promoting effects of modafinil were modest, and the wake promoting effect of 200 mg/kg of modafinil roughly corresponds to 50 mg/kg of test compound. However, modafinil did not strongly reduce REM sleep after the administration of 50 mg/kg of test compound. Furthermore, test compound potently reduced REM sleep, and this contrasts to the effects of modafinil.

Effects on Sleep During the Active Period:

The same experiment was repeated by administrating compounds in the active period. During the active period, narcoleptic mice spend more in sleep than wild-type mice. Wild-type animals typically stayed awake for almost three hours after vehicle administration. Similar to the effects observed during the light period, test compound dose-dependently increased wakefulness in both wild and narcoleptic mice. Wake-promoting effects in wild-type mice were however, subtle during the dark period due to the high amount of wakefulness at the baseline, and only small effects were observed. In contrast, much pronounced wake-promoting effects were observed in narcoleptic mice, and wake amounts in these mice after 100 and 150 mg/kg test compound administration were brought up to the levels of wild-type mice, suggesting that this compound normalizes the sleep/wake amount of narcoleptic mice. Similarly non-REM and REM sleep were reduced in narcoleptic mice by test compound and the amounts of non-REM and REM sleep were also brought down to the levels of wild-type mice. Similar, but much weaker effects were also seen after modafinil administration in these mice. Although modafinil dose-dependently increase wakefulness in narcoleptic mice, the high dose of modafinil (200 mg/kg) did not bring the wake amount to that of the wild-type baseline levels.

References Cited

All references cited herein are incorporated herein by reference in their entirety and for all purposes to the same extent as if each individual publication or patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety for all purposes.

The discussion of references herein is intended merely to summarize the assertions made by their authors and no admission is made that any reference constitutes prior art. Applicants reserve the right to challenge the accuracy and pertinence of the cited references.

The present invention is not to be limited in terms of the particular embodiments described in this application, which are intended as single illustrations of individual aspects of the invention. Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatus within the scope of the invention, in addition to those enumerated herein will be apparent to those skilled in the art from the foregoing description. Such modifications and variations are intended to fall within the scope of the appended claims. The present invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. 

What is claimed is:
 1. A method of treating restless legs syndrome, comprising the administration of a therapeutically effective amount of a compound having structural Formula (1) or a pharmaceutically acceptable salt or amide thereof, to a mammal in need of treatment:

wherein, R₁ and R₂ are hydrogen and the compound of structural Formula (1) is an enantiomeric mixture wherein the (R) enantiomer of the compound predominates.
 2. The method of claim 1, wherein the (R) enantiomer predominates to the extent of about 90% or greater.
 3. The method of claim 2, wherein the (R) enantiomer predominates to the extent of about 98% or greater.
 4. A method of treating restless legs syndrome comprising the administration of a therapeutically effective amount of a compound having structural Formula (1) or a pharmaceutically acceptable salt thereof, to a mammal in need of treatment:

wherein, R₁ and R₂ are hydrogen; and the compound of structural Formula (1) is the (R) enantiomer substantially free of other enantiomers. 